Overview

Brief Summary

Bank voles are more climbers than diggers. Nevertheless, they usually build their nest in a hole under the ground.They aren't easily frightened and are readily seen. They live more above ground and are active mostly during the day than other voles. Bank voles eat mostly grass, seeds and fruits, supplemented with worms, spiders and insects.

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Biology

Bank voles are active during both the day and night, although they become increasingly nocturnal during the summer (4). They do not hibernate in winter, but are active throughout the year (4). They have a broad diet, which is mainly herbivorous, including fruit, soft seeds, leaves, fungi, roots, grass, buds and moss. They may also occasionally take invertebrate food such as snails, worms and insects (4), and the odd bird egg may be eaten (2). Breeding typically takes place between April and October, but when conditions are suitable, births may occur throughout the year (4). Ovulation by the female is stimulated by the presence of a male, possibly via certain scents that males produce (5). Gestation takes around 21 days, but may be a short as 17 days in this species if conditions are optimal (5). Between 4 and 5 litters are produced in a year, each one consisting of 3-5 young (4). Females are able to conceive again whilst still suckling the previous litter; under these circumstances the gestation period will be longer, up to 24 days (5). The young voles are born in a nest, which is usually located underground (5). Males do not assist with rearing the offspring. Females are very protective of the litter; if any young leave the nest the female locates them and carries them back to the nest (5). The young become sexually mature at around 4.5 weeks of age, however those born later in the year will not start to breed until the next spring (4). Predators such as owls, kestrels, foxes and weasels take their toll on vole populations; the maximum life span for this species is 18 months. The numbers of bank voles varies greatly throughout the year, being high towards the end of summer and plummeting through the winter to a low in April (4).

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Description

The bank vole has a small, stocky body and a blunt, rounded muzzle (2). The upperparts may be yellowish, reddish or brown in colour, the flanks are greyish and the rump is whitish-grey (2). The short tail is usually slightly bushy at the tip (2).

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Distribution

Range Description

The bank vole, Myodes glareolus has a wide range in the Palaearctic which stretches from the British Isles through continental Europe and Russia to Lake Baikal. In the north, its range extends beyond the Arctic circle, and in the south it reaches northern Turkey and northern Kazakhstan (Shenbrot and Krasnov 2005). It is widespread in Europe, although it is absent from southern Iberia and the Mediterranean islands. It is found from sea level to 2,400 m (Spitzenberger 1999).

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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Europe, parts of Asia Minor, and central Asia (Nowak 1991). Introduced and established in Ireland (Nowak 1991) and Newfoundland (Joe Brazil, pers. comm., 2000). Brazil last checked the population on Yellow Fox Island, Notre Dame Bay, Newfoundland, in 1986. Specimens from that survey are in the National Museum in Ottawa, the Newfoundland Museum in St. John's, and in Brazil's possession. This vole was introduced to this small island in the mid- to late 1960s by Dr. Bill Pruitt and/or one of his students. The island is not large, less than a square kilometer. Brazil stated he had no reason to believe that the voles are not still thiving on the island. They have no competitors and few if any predators.

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Range

Common in Britain, including a number of the islands. On Skomer Island off the Pembrokeshire coast of Wales, there is a subspecies known as the Skomer vole (Clethrionomys glareolus skomerensis). The bank vole is also common throughout much of western and central Europe (4).

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Physical Description

Morphology

Adult bank voles reach a head-body length of 10-11cm and a weight of 17-20g, with males and females being approximately the same size. The tail is less than body length and reaches a length of 3-4cm. Bank voles are small with small eyes and ears. Their body is covered by thick fur in shades of brown or gray. Their muzzle is blunt and rounded. Relative to body size, M. glareolus has a small brain. Teeth are prismatic and are characterized by flat crowns, which are adapted for their herbivorous diet (Macdonald 2001).

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Ecology

Habitat

Habitat and Ecology

It inhabits all kinds of woodland, preferring densely-vegetated clearings, woodland edge, and river and stream banks in forests. It is also found in scrub, parkland, and hedges (Viro and Niethammer 1982, Spitzenberger 1999).

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Trophic Strategy

Myodes glareolus have been characterized as omnivorous (Ostfeld 1985) and herbivorous (Macdonald 2001). When eating grass, M. glareolus clip the stalks and lays the clippings in piles. Food is obtained in the winter by burrowing underground. In the summer and fall food is cached. Diet changes with season and location but includes green parts of plants (Macdonald 2001), fruits and seeds from available trees, such as the European ash tree (Fraxinus excelsior) (Flowerdew and Gardner 1978) and grass (Macdonald 2001).

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Associations

Bank voles are important as a prey base for many small avian and mammalian predators and snakes. They are often abundant and can form the main component of the diet of these predators. They may also help in recycling and redistributing nutrients in the ecosystems in which they live through herbivory.

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Many small predators rely on bank voles as prey. Bank voles partially escape predation by remaining under cover in underground tunnels or runways in grass and vegetation. I is thought that avian predators use the ultraviolet reflections of scent marks to locate their prey (Koivula et al. 1999).

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Life Expectancy

The lifespan of M. glareolus is very short. Average lifespan is 0.5-2 years, with most individuals not lasting more than one breeding season (Macdonald 2001; Ostfeld 1985). Bank voles mature quickly with females maturing at 2-3 weeks and males maturing at 6-8 weeks (Macdonald 2001).

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Reproduction

The mating system of M. glareolus can be described as polygamous (Macdonald 2001), and possibly promiscuous (Horne and Ylonen 1998). While females defend territories that may overlap with other females, males defend larger territories that overlap with the territories of several females. Females appear to prefer dominant males and may affect which males get the chance to mate by running away from subordinate males (Horne and Ylonen 1998). As parturition nears, females become more aggressive and each female's territory decreases in size. The home range becomes smaller and the central ranges of different territories become farther from each other (Koskela et al. 1997).

Mating System: polygynous ; polygynandrous (promiscuous)

The estrous cycle of M. glareolus lasts four days (Oksanen et al. 1999). The breeding season is from late April to September (Oksanen et al. 2001). Copulation is characterized by a series of intromissions followed by ejaculation (Horne and Ylonen 1996). Gestation lasts from 17 days with optimal nutrition, to 24 days if the female becomes pregnant while lactating during postpartum estrus (Macdonald 2001; Koskela et al. 1998). The average gestation length is 21 days (Macdonald 2001). From 1 to 10 pups are born per litter with approximately 4 litters born per breeding season (Macdonald 2001; Oksanen et al. 2001). The average number of pups per litter is 4-8 (Oksanen et al. 2001). Pups weigh 1-10g at birth, which makes up a total of 22-28% of the female’s weight. During pregnancy and lactation, females require 30-130% more energy (Ostfeld 1985). Infanticide occurs in males and females. Females will kill the pups of their female neighbors and males will kill pups as a mating tactic (Koskela et al. 1998; Koskela et al. 1997; Horne and Ylonen 1996).

Pups are born blind and helpless in an underground nest lined with grass and other vegetation. The female is the sole provider of parental care (Macdonald 2001). The pups are weaned at the age of 20-25 days (Macdonald 2001; Oksanen et al. 2001; Oksanen et al. 1999; Horne and Ylonen 1998).

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Trends

Population

It is very common throughout much of its European range, with typical densities varying between approximately 6-12 individuals per hectare and 50-100 individuals per hectare (Spitzenberger 1999). Populations densities fluctuate from year to year. The long-term trend appears stable.

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Where they occur in close proximity to roads, bank voles may be at risk from lead exposure. In agricultural areas, pesticide drift, and exposure to molluscicides and rodenticides may all pose threats. The fragmentation of woodlands, removal of hedgerows and overgrazing of herbaceous ground cover by deer reduce the chances of bank voles persisting in an area (4).

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Wikipedia

Bank vole

The bank vole (Myodes glareolus; formerly Clethrionomys glareolus) is a small vole with red-brown fur and some grey patches, with a tail about half as long as its body. A rodent, it lives in woodland areas and is around 100 millimetres (3.9 in) in length. The bank vole is found in western Europe and northern Asia. It is native to Great Britain but not to Ireland, where it has been accidentally introduced, and has now colonised much of the south and southwest.

The bank vole lives in woodland, hedgerows and other dense vegetation such as bracken and bramble. Its underground chamber is lined with moss, feathers and vegetable fibre and contains a store of food. It can live for eighteen months to two years and is mostly herbivorous, eating buds, bark, seeds, leaves and fruits and occasionally insects and other small invertebrates. It readily climbs into scrub and low branches of trees. It breeds in shallow burrows, the female rearing about four litters of pups during the summer.

Contents

The bank vole is a small rodent resembling a mouse but with a stouter body, a slightly rounder head with smaller ears and eyes and a shorter, hairy tail. The dorsal surface is reddish-brown, with a greyish undercoat and the flanks are grey with a reddish-brown sheen. The underparts are whitish-grey sometimes tinged with dull yellow. The ears are larger than those of most voles. The adult head and body length varies between 3.25 and 4.75 inches (83 and 121 mm) and the tail ranges from 1.5 to 3 inches (38 to 76 mm). The weight is between 15.4 and 36 grams (0.54 and 1.27 oz). Young animals are darker in colour with greyer underparts. The bank vole is capable of making growling sounds and can utter low-pitched squeaks.[2]

In areas such as Great Britain, where the only other small vole is the short-tailed vole (Microtus agrestis), the bank vole is distinguished by its more prominent ears, chestnut-brown fur and longer tail. The northern red-backed vole (Myodes rutilus) from northern Scandinavia and Russia, has a shorter tail and is paler with less grey in its pelage. The grey red-backed vole (Myodes rufocanus) from northern Eurasia, is larger with a distinctive reddish back.[2]

The bank vole has a palearctic distribution. It is native to Europe, Asia Minor and parts of Western Siberia. It does not occur in Iceland, Ireland or northern Scandinavia (except for Finland) and is absent from the Iberian Peninsula and most of Italy.[2] It was introduced into south western Ireland in the 1950s where it has taken hold and there are fears that it may be displacing the native wood mouse (Apodemus sylvaticus). A subspecies found on the island of Skomer in West Wales, the Skomer vole (Myodes glareolus skomerensis), is much larger than the mainland bank vole and there may be 20,000 individuals on the island in late summer.[3]

The bank vole is found in forests, especially in deciduous and mixed woodland with scrub, low plants and leaf litter. It is also present in hedgerows, field verges, among bracken and brambles, river banks, swamps and parks. In mountainous regions and the northern part of its range it occurs in coniferous woodland at altitudes of up to 1,800 metres (5,900 ft). It is not found on bare soil and ample ground cover seems a necessity.[2] In the Mediterranean region, at the southern extent of its range, it is a habitat specialist and is found in moist woodland but not in grassland and bushy places.[4] At the fringes of forested areas it is possible for there to be a metapopulation consisting of a number of spatially separated populations of bank vole that come and go according to the season and local events. Some areas may be devoid of voles during the winter and be repopulated during the summer only to become empty of voles again in October. The further from permanently inhabited forest the location is, the fewer females there are and the more widely does the number of individuals fluctuate.[5]

The bank vole is active by day and also at night and it does not hibernate in winter. It excavates long, shallow branching burrows with multiple exits, sometimes tunelling along beneath the leaf litter. It gathers and stores food underground and makes a nest with moss, dry grasses and leaves close to the surface or even above ground. It is in general quite bold but is also very alert to the cries of other animals such as tits warning of aerial predators.[2]

The bank vole is primarily a herbivore. Its diet varies with the season but usually consists of leaves, grasses, roots, buds, bark, fruits, nuts, grain and seeds. When feeding on grass stalks it may clip the stalks and lay the cut pieces in piles. Some food is carried back to the burrow where it is kept in dedicated storage chambers. It sometimes eats animal food in the form of insects, spiders and worms and may take eggs from the nests of birds nesting on the ground.[2][6]

The bank vole climbs well and in the winter it feeds on the bark of trees including beeches, maples and larch up to several metres above the ground. It also eats tree seedlings and reduces the natural regeneration of woodland and when present in large numbers, is considered a forest pest. However, its harmfulness is relatively low in a healthy ecosystem because significant damage only occurs when numbers build up, and because it has a large number of natural enemies its population is normally kept under control.[7]

Females maintain territories which may overlap somewhat, and males occupy larger territories covering those of several females. The home range of females is usually between 500 and 2,000 square metres (5,400 and 21,500 sq ft).[8] The breeding season lasts from Late April to September. Females appear to prefer dominant males and may actively avoid other vagrant males. The gestation period averages 21 days, being longer if the female is still lactating from a previous litter. A litter can be up to ten pups but the average number is four to eight. Females sometimes kill pups in burrows in adjoining territories and males sometimes kill pups before mating with their mother, perhaps as a tactic to ensure his offspring are advantaged. The pups are naked and helpless and their eyes open at about nine days. They are weaned at 20 to 25 days and the females become sexually mature by six weeks with the males reaching maturity by eight weeks. There may be up to four litters per year and as the youngsters start to breed, numbers quickly build up over the summer months. The bank vole lives for up to two years.[6]

The bank vole is plentiful during much of the year and plays an important part in the diet of various predators including the red fox (Vulpes vulpes), the stoat (Mustela erminea), the least weasel (Mustela nivalis), the European mink (Mustela lutreola), the common kestrel (Falco tinnunculus), the rough-legged buzzard (Buteo lagopus) and the tawny owl (Strix aluco). The voles try to prevent being caught by avoiding open areas of ground, by using underground tunnels and well-worn paths through the undergrowth.[6]

The bank vole acts as a reservoir on infection for the Puumala virus, which can infect humans, causing a haemorrhagic fever known as nephropathia epidemica and, in extreme cases, even death.[9] Although this hantavirus has co-evolved with its host, its presence among populations seems to decrease their over-winter survival rates.[10]

^Yeron Kalner (August 7, 2014) "Deadly Research," Retrieved Yedioth Ahronoth, p. 27, announced the death of Dr. Keren Ambar, a post-graduate studying the behavior of the bank vole in Finland. She had been affected by the Puumala virus which caused a complete breakdown of her immune system.